A conventional battery charger has a voltage converter configured to convert an incoming supply voltage to an output voltage suitable for a connectable battery. The current delivered to the battery from the voltage converter is a function of the output resistance of the battery charger and the resistance of the battery. This means that a battery charger with a low output resistance will deliver a high amount of output current without too much output voltage losses. A high amount of output current is desired when the battery is large with a low resistance. However, if a small battery is connected to a powerful battery charger several problems arise, such as for example overheating of the battery due to a large charging current.
Within the field of battery technology it is common to use a specific notation for currents and capacities. The capacity of a battery is normally given as ampere×hours [Ah]. A small lead acid battery might have a capacity C=12 Ah. A common way to describe a given current is to use the notation C/X, where X=1 . . . 100 hours. For example if this small battery is discharged at C/20 hours rate, the discharge current from the battery would be 12 Ah/20 h=0.6 A. For comparison, if a large battery with a capacity of 180 Ah is discharged at the same C/20 rate, the discharge current would be 180 Ah/20 h=9 A. Thus by expressing the current as C/20, the current becomes a function of the battery capacity, which is suitable for comparing batteries with different sizes and capacities.
In a modern workshop it is convenient to have one battery charger configurable for charging all types of batteries and all battery sizes from small motorcycle batteries (12 Ah) to large truck batteries (180 Ah). In a conventional workshop battery charger it is common that the charging current must be manually selected and a rule of thumb for calculating the charging current is that the charging current could be C/10, i.e. 10% of the battery capacity. This means that for a 75 Ah battery the charging current should be adjusted to 7.5 A. In order to fully charge a 75 Ah battery, 10 hours at 7.5 A is required using a simple rule of thumb for calculation, not including the current state of charge of the battery. If a service technician by mistake connects the battery charger which is adjusted for a truck battery, to a much smaller battery a very dangerous situation would occur that in best case could lead to a damaged battery and in worst case could lead to a fire in the workshop or in the vehicle.
This rough estimation of charging current and charging time, based on the rule of thumbs described above does not take into account the current state of charge of the battery. Therefore, it is easy to overcharge the battery with the associated evolution of gas from the battery.
It is therefore of great importance to find a solution that could prevent this disastrous situation by means of automatically adjusting the charging current and time.
An example of an adaptive battery charger is disclosed in U.S. Pat. No. 5,160,880. However, the method disclosed in U.S. Pat. No. 5,160,880 is very slow due to the determination of the gas point of the connected battery.
It is an object of the present invention to provide an improved method for charging the battery.
A further object is to provide a more optimum charging method that reduces the risk of increased gas emission and overheating of the battery, as well as a battery charger therefor.
An additional object is to provide a fast method for charging a battery, as well as a battery charger therefore.